Erwan Gouranton

Beta-Carotene Reduces Body Adiposity of Mice via BCMO1

Evidence from cell culture studies indicates that β-carotene-(BC)-derived apocarotenoid signaling molecules can modulate the activities of nuclear receptors that regulate many aspects of adipocyte physiology. Two BC metabolizing enzymes, the BC-15,15′-oxygenase (Bcmo1) and the BC-9′,10′-oxygenase (Bcdo2) are expressed in adipocytes. Bcmo1 catalyzes the conversion of BC into retinaldehyde and Bcdo2 into β-10′-apocarotenal and β-ionone. Here we analyzed the impact of BC on body adiposity of mice. To genetically dissect the roles of Bcmo1 and Bcdo2 in this process, we used wild-type and Bcmo1 -/- mice for this study. In wild-type mice, BC was converted into retinoids. In contrast, Bcmo1-/- mice showed increased expression of Bcdo2 in adipocytes and β-10′-apocarotenol accumulated as the major BC derivative. In wild-type mice, BC significantly reduced body adiposity (by 28%), leptinemia and adipocyte size. Genome wide microarray analysis of inguinal white adipose tissue revealed a generalized decrease of mRNA expression of peroxisome proliferator-activated receptor γ (PPARγ) target genes. Consistently, the expression of this key transcription factor for lipogenesis was significantly reduced both on the mRNA and protein levels. Despite β-10′-apocarotenoid production, this effect of BC was absent in Bcmo1-/- mice, demonstrating that it was dependent on the Bcmo1-mediated production of retinoids. Our study evidences an important role of BC for the control of body adiposity in mice and identifies Bcmo1 as critical molecular player for the regulation of PPARγ activity in adipocytes

Adiponectin Expression Is Induced by Vitamin E via a Peroxisome Proliferator-Activated Receptor γ-Dependent Mechanism

Adiponectin is a well-known adipokine secreted by adipocytes that presents insulin-sensitizing properties. The regulation of expression of this adipokine by micronutrients is largely unknown. We demonstrate here that adiponectin expression is induced in adipocytes after exposure to tocopherols via the peroxisome proliferator-activated receptor gamma (PPARgamma) pathway. Vitamin E force feeding resulted in an induction of adiponectin in mice at both mRNA and protein levels. Adiponectin mRNA and protein secretion were also increased by vitamin E (alpha- and gamma-tocopherol) in 3T3-L1 cells, together with PPARgamma mRNA, independent of an antioxidant effect. In transient transfections, both alpha- and gamma-vitamers induced the luciferase gene reporter under the control of a human adiponectin promoter via a PPAR-responsive element. The induction of adiponectin by tocopherols seems to be PPARgamma dependent, because it was blocked by the specific antagonist GW9662. Finally, we showed that intracellular concentrations of a PPARgamma endogenous ligand, 15-deoxy-Delta12,14-prostaglandin J2, increased after treatment with tocopherols in 3T3-L1 cells. In summary, vitamin E up-regulates adiponectin expression via a mechanism that implicates PPARgamma together with its endogenous ligand 15-deoxy-Delta12,14-prostaglandin J2. The induction of adiponectin via an original molecular mechanism could be considered as the basis for the beneficial effect of vitamin E on insulin sensitivity.

Vitamin D reduces the inflammatory response and restores glucose uptake in adipocytes.

SCOPE Obesity is strongly associated with low-grade inflammation, notably due to an overproduction of proinflammatory markers by adipose tissue and adipocytes as well as a vitamin D deficiency. Whether these problems are interrelated has not been clearly established. METHODS AND RESULTS In the present report, decreases in the levels of inflammatory markers such as IL-6, MCP-1, and IL-1β (mRNA and protein level) in human adipocytes and in 3T3-L1 adipocytes were observed after 1,25-dihydroxyvitamin D3 (1,25-(OH)(2) D(3) ) treatment. Such treatment also decreased the expression of the TNF-α-mediated proinflammatory marker in 3T3-L1 and human adipocytes. A similar effect was observed in adipocyte-macrophage co-culture systems in which 1,25-(OH)(2) D(3) decreased proinflammatory marker expression under basal and TNF-α-stimulated conditions. The involvement of VDR and NF-κB was confirmed in these regulations. Incubation with 1,25-(OH)(2) D(3) also resulted in the dephosphorylation of p38, which is linked to the transcriptional induction of several Dusp family members. Functional consequences of the 1,25-(OH)(2) D(3) treatment on glucose uptake and AKT phosphorylation were observed. CONCLUSION The improvement of both proinflammatory status and glucose uptake in adipocytes under 1,25-(OH)(2) D(3) effect suggests that low-grade inflammation could be linked to vitamin D deficiency. This observation offers new perspectives in the context of obesity and associated physiopathological disorders.

Lycopene attenuates LPS-induced TNF-α secretion in macrophages and inflammatory markers in adipocytes exposed to macrophage-conditioned media

SCOPE Adipose tissue is infiltrated by an increasing number of macrophages during the development of obesity. These immune cells are suspected to be a major source of TNF-α that interferes with adipocyte function. Because lycopene possesses anti-inflammatory properties, we hypothesize that lycopene could reduce the production of TNF-α by macrophages and thus interfere in the cross-talk between macrophages and adipocytes. METHODS AND RESULTS We demonstrated that physiological concentrations of lycopene were able to attenuate the lipopolysaccharide (LPS)-mediated induction of TNF-α in RAW 264.7 macrophages, at both the mRNA and protein levels. The molecular mechanism was studied. It appeared that the LPS-activation of both JNK and NF-κB signaling pathways was modulated by lycopene. The anti-inflammatory effects of lycopene on macrophages were accompanied by a decrease in LPS-stimulated macrophage migration in the presence of lycopene. Furthermore, lycopene decreased macrophage conditioned medium-induced proinflammatory cytokine, acute phase protein, and chemokine mRNA expression in 3T3-L1 adipocytes. CONCLUSION These data indicate that lycopene displayed an anti-inflammatory effect on macrophages that beneficially impacted adipocyte function. Thus, these results suggest that lycopene could block the vicious cycle that occurs between adipocytes and macrophages in adipose tissue during obesity.

Vitamin E decreases endogenous cholesterol synthesis and apo-AI-mediated cholesterol secretion in Caco-2 cells☆

Intestine is the gateway for newly absorbed tocopherols. This organ also plays a crucial role in cholesterol metabolism. Because tocopherols are known to impact cholesterol metabolism in the liver, we hypothesized that tocopherols could also modulate cholesterol metabolism in the intestine. This study aimed to verify this hypothesis and to unveil the mechanisms involved, using Caco-2 cells as a model of the human intestinal cell. Both α- and γ-tocopherol significantly (P<.05) decreased endogenous cholesterol synthesis and apo-AI-mediated cholesterol secretion in Caco-2 cells. Tocopherols down-regulated (P<.05) up to half of the genes involved in the cholesterol synthesis pathway, together with CYP27A1, which is involved in oxysterol production. The activity of this enzyme, as well as the levels of intracellular oxysterols, was significantly diminished by tocopherols. Finally, tocopherols significantly reduced ABCA1 mRNA levels in Caco-2 cells. We conclude that tocopherols impair the endogenous synthesis and apo-AI-mediated secretion of cholesterol in Caco-2 cells. This effect involves a down-regulation of genes involved in the cholesterol synthesis pathway, resulting in down-regulation of CYP27A1 which, in turn, diminishes oxysterol concentrations. The outcome is a decrease of LXR activity, resulting in down-regulation of ABCA1. These data reinforce the effect of α- and γ-tocopherol on cholesterol metabolism via gene expression regulation.

Chemokine Expression in Inflamed Adipose Tissue Is Mainly Mediated by NF-κB

Immune cell infiltration of expanding adipose tissue during obesity and its role in insulin resistance has been described and involves chemokines. However, studies so far have focused on a single chemokine or its receptor (especially CCL2 and CCL5) whereas redundant functions of chemokines have been described. The objective of this work was to explore the expression of chemokines in inflamed adipose tissue in obesity. Human and mouse adipocytes were analyzed for expression of chemokines in response to inflammatory signal (TNF-α) using microarrays and gene set enrichment analysis. Gene expression was verified by qRT-PCR. Chemokine protein was determined in culture medium with ELISA. Chemokine expression was investigated in human subcutaneous adipose tissue biopsies and mechanism of chemokine expression was investigated using chemical inhibitors and cellular and animal transgenic models. Chemokine encoding genes were the most responsive genes in TNF-α treated human and mouse adipocytes. mRNA and protein of 34 chemokine genes were induced in a dose-dependent manner in the culture system. Furthermore, expression of those chemokines was elevated in human obese adipose tissue. Finally, chemokine expression was reduced by NF-κB inactivation and elevated by NF-κB activation. Our data indicate that besides CCL2 and CCL5, numerous other chemokines such as CCL19 are expressed by adipocytes under obesity-associated chronic inflammation. Their expression is regulated predominantly by NF-κB. Those chemokines could be involved in the initiation of infiltration of leukocytes into obese adipose tissue.

β-Carotene conversion products and their effects on adipose tissue

Recent epidemiological data suggest that β-carotene may be protective against metabolic diseases in which adipose tissue plays a key role. Adipose tissue constitutes the major β-carotene storage tissue and its functions have been shown to be modulated in response to β-carotene breakdown products, especially retinal produced after cleavage by β-carotene 15,15′-monooxygenase (BCMO1), and retinoic acid arising from oxidation of retinal. However, the possibility exists that β-carotene in its intact form can also affect adipocyte function. Development of a knock out model and identification of a loss-of-function mutation have pointed out BCMO1 as being probably the sole enzyme responsible for provitamin A conversion into retinal in mammals. The utilisation of BCMO1−/−mice should provide insights on β-carotene effect on its own in the future. In humans, intervention studies have highlighted the huge interindividual variation of β-carotene conversion efficiency, possibly due to genetic polymorphisms, which might impact on response to β-carotene. This brief review discusses the processes involved in β-carotene conversion and the effect of cleavage products on body fat and adipose tissue function.

Purified low-density lipoprotein and bovine serum albumin efficiency to internalise lycopene into adipocytes

Epidemiological studies have suggested that lycopene has protective effects against various diseases including cardiovascular diseases. However, mechanistic studies to understand these effects are difficult due to the insolubility of lycopene in aqueous culture medium. The objective of the present study was to use LDL or BSA as physiological vehicles for lycopene and to compare them with various classical vehicles. Among tested vehicles, only LDL, BSA, THF/BHT, beadlets, and liposomes were able to solubilise lycopene. No cytotoxicity was observed with these vehicles. LDL and BSA allowed good stability of lycopene during incubation (52% and 43% for 2microM lycopene solutions), but remained less efficient than THF/BHT or beadlets (67% and 62%). Incubation of adipocytes (3T3-L1) with the different vehicles for 24 and 48h showed that beadlets best delivered lycopene to cells. Finally, whatever the vehicle used, intracellular localization of lycopene was the same: lipid droplets (32-51%), plasma membrane (32-37%) and nuclear membrane (19-29%). As a conclusion, LDL or BSA display comparable properties to THF/BHT or beadlets. It is the first time that lycopene carried by physiological vehicles is shown to reach different subcellular compartments supporting molecular effects in adipocyte, such as cell signaling or nuclear receptor interacting.

All-trans retinoic acid induces oxidative phosphorylation and mitochondria biogenesis in adipocytes.

A positive effect of all-trans retinoic acid (ATRA) on white adipose tissue (WAT) oxidative and thermogenic capacity has been described and linked to an in vivo fat-lowering effect of ATRA in mice. However, little is known about the effects of ATRA on mitochondria in white fat. Our objective has been to characterize the effect of ATRA on mitochondria biogenesis and oxidative phosphorylation (OXPHOS) capacity in mature white adipocytes. Transcriptome analysis, oxygraphy, analysis of mitochondrial DNA (mtDNA), and flow cytometry-based analysis of mitochondria density were performed in mature 3T3-L1 adipocytes after 24 h incubation with ATRA (2 µM) or vehicle. Selected genes linked to mitochondria biogenesis and function and mitochondria immunostaining were analyzed in WAT tissues of ATRA-treated as compared with vehicle-treated mice. ATRA upregulated the expression of a large set of genes linked to mtDNA replication and transcription, mitochondrial biogenesis, and OXPHOS in adipocytes, as indicated by transcriptome analysis. Oxygen consumption rate, mtDNA content, and staining of mitochondria were increased in the ATRA-treated adipocytes. Similar results were obtained in WAT depots of ATRA-treated mice. We conclude that ATRA impacts mitochondria in adipocytes, leading to increased OXPHOS capacity and mitochondrial content in these cells.

Visfatin is involved in TNFα-mediated insulin resistance via an NAD+/Sirt1/PTP1B pathway in 3T3-L1 adipocytes

Tumor necrosis factor α (TNFα) is a well-known mediator of inflammation in the context of obesity in adipose tissue. Its action appears to be directly linked to perturbations of the insulin pathway, leading to the development of insulin resistance. Visfatin has been suspected to be linked to insulin sensitivity, but the mechanism involved is still partly unknown. The aim of this study was to evaluate the role of visfatin in the impairment of the insulin pathway by TNFα activity in 3T3-L1 adipocytes and to unveil the mechanisms involved in such impairment. We demonstrated in 3T3-L1 adipocytes that visfatin was involved in TNFα-mediated insulin resistance in adipocytes. Indeed, after TNFα treatment in 3T3-L1 cells, visfatin was downregulated, leading to decreased nicotinamide adenine dinucleotide (NAD+) concentrations in cells. This decrease was followed by a decrease in Sirt1 activity, which was linked to an increase in PTP1B expression. The modulation of PTP1B by visfatin was likely responsible for the observed decreases in glucose uptake and Akt phosphorylation in 3T3-L1 adipocytes. Here, we demonstrated a complete pathway involving visfatin, NAD+, Sirt1, and PTP1B that led to the perturbation of insulin signaling by TNFα in 3T3-L1 adipocytes.